Inventors have long sought to provide a system of associated devices for effectively monitoring the condition of a diaper, other undergarment, bedding or the like. While the present invention provides an elimination-absorber monitoring system useful in each of these environments, a preferred embodiment is utilized in conjunction with a disposable diaper. Thus, for purposes of brevity in the present specification, the term “diaper” shall indicate any of the above-described use environments, except where otherwise specifically stated or apparent from context.
The art is replete with examples of prior attempts to satisfy the need for an elimination-absorber monitoring system. Each has, for one reason or another, apparently failed to achieve significant implementation and consumer acceptance. Upon review, the prior systems appear either impractical, unsuitable to the use environment, unworkable and/or uneconomical—largely for one or more of the following reasons: failure to provide an appropriate sensor response or alarm criteria with respect to urine-soiling; inability to detect fecal matter, or to provide an appropriate sensor response or alarm criteria with respect to feces-soiling; lack of important user-oriented features; and unsuitability to cost-effective manufacturing.
Most previous systems have utilized the measurement of electrical conductivity between two spaced electrodes disposed somewhere on top of, within, or under the absorbent layers of a diaper, to detect the presence of liquid urine when it bridged some path between the electrodes. This approach is described in U.S. Pat. No. 3,460,123 (Bass), U.S. Pat. No. 4,356,818 (Macias), U.S. Pat. No. 4,800,370 (Vetecnik), U.S. Pat. No. 4,539,559 (Kelly), U.S. Pat. No. 4,768,023 (Xie), U.S. Pat. No. 5,036,859 (Brown), U.S. Pat. Nos. 5,264,830 and 5,392,032 (Kline), U.S. Pat. No. 4,205,672 (Dvorak), and U.S. Pat. Nos. 5,266,928 and 5,395,358 (Lu). These systems all depended on the relatively high conductivity of urine, as compared to the typically low conductivity of unsoiled, dry diaper materials. Several of these prior inventors clearly assumed that the key to a useful “diaper wetness” alarm (as their objective was often termed) would be the detection of virtually any urine in a diaper. They also recognized that, depending on the sensor configuration, urine could miss the intended target. Thus, variations of this approach incorporated either distributed (e.g., screen-like) electrodes or various absorbent pads or modifications of a diaper to help collect, funnel or direct urine flow to bridge the sensing electrodes, e.g., U.S. Pat. No. 4,356,818 (Macias). However, this focus on the detection of simple “wetness” resultant from urination—as opposed to the far more useful determination that an elimination-absorber actually required changing (or at least inspection)—failed to answer the real needs of caregivers and diaper-wearers. As with all the prior systems, seemingly little emphasis was placed on defining and obtaining truly user-responsive sensor performance. While this simple “wetness detection” focus may have appeared somewhat workable, as applied to certain cloth or early low-absorbency diapers, it did not adequately address the effects of widely differing flow-rates and volumes in various urination events and situations. Moreover, for reasons that shall be explained below, this approach was completely incompatible with the properties (and particularly the much greater capacity) of modern disposable diapers. Thus, previous systems based on simple “wetness detection” typically either failed to work consistently, or were prone to meaningless or premature alarm indications.
Some prior attempts took the view that a “soiled” diaper condition could be deduced by simply detecting the arrival of urine at the bottom (just inside the outer cover) of a diaper, i.e., that this would indicate when the diaper had reached its absorbent capacity. However, high-absorbency diapers are specifically designed to prevent urine from soaking to the outer cover, at least during the expected wearing time. Because urine permeates into and through a diaper with at least some time delay, additional urine will continue to collect after it first reaches a pair of sensing electrodes. If urine is detected only after soaking to the bottom of a diaper, the continued accumulation will tend to quickly spread along the inside of the cover, and quite likely leak out before the diaper can be changed. Thus, the determination of a fully saturated condition based on the sudden presence of urine at the bottom layers is not practically useful. Even completely non-electronic approaches to diaper monitoring, such as the “happy face” visual indicators incorporated into the outer cover of Fitti™ brand diapers, can similarly suffer from the limitations of over-simplified alarm criteria and inappropriate, inconsistent, or untimely sensor response. Also, such purely visual wetness-indicating devices, which are necessarily disposed directly on a diaper cover, have limited value for other reasons. Just as with traditional methods, they still require frequent and continual checking by a caregiver—and the awkward removal of clothing layers worn over a diaper—to permit viewing of the indicator. They thereby fail to provide a convenient, automatic, attention-getting signal that a diaper needs changing.
Still other inventors tried to “intercept” the flow of urine somewhere in the mid-layers of a diaper, but as will be appreciated by those skilled in the art, another problem results from the modern disposable diaper being such an aggressive absorber. No choice of conductivity-sensing path within such diapers (including midway through the absorbent layers) is likely to conveniently go from “dry” to fully “wet” at such time as to appropriately reflect a “needs to be changed” condition. In some such diapers, “super-absorbent” particles or polymer jells have been used to dramatically increase the liquid-holding capacity in a central core of the absorbent structure. These central absorbers are typically surrounded by conventional (e.g., cellulose based) absorbent wadding because the super-absorbers tend to react relatively slowly in absorbing liquid, as compared to the conventional materials. This means that the distribution of liquid through the diaper is highly non-uniform and it changes markedly after a urination event, as the super-absorber core gradually pulls liquid out of the conventional absorbent bulk. Also, with intermediate levels of moisture in any type of diaper (where the absorbent material is not yet completely saturated), urine can accumulate gradually or unevenly—often separated into discontinuous droplets or unpredictably scattered wet or merely damp regions. Thus, these regions may not happen to span a chosen path between electrodes so that the urine can be reliably detected. Moreover, the mere presence of relatively high conductivity (and hence the presence of liquid) along any given path through a diaper may not reflect a true “needs to be changed” condition (i.e., correlate with caregiver expectations or with traditional diaper inspection methods), particularly in the case of modern high-absorbency, disposable diapers. As explained above, none of the foregoing simple conductivity-based systems reflected a truly appropriate sensor response or “alarm criteria” with respect to urine-soiling of diapers. They typically responded either immediately or prematurely to the presence of trivial amounts of urine passing into a diaper; or alternatively, they responded either inconsistently, or not until after the diaper was soaked beyond its safe absorbent capacity—depending primarily on the choice of sensing location.
Other prior devices have measured AC-conductivity (or related electrical capacitance) across a bulk volume of diaper absorbent material, to achieve more appropriate alarm indications, e.g., U.S. Pat. Nos. 4,704,108 and 4,754,264 (Okada). These methods employed indirect determination of the average “moisture content” or “dampness” in some portion of the diaper absorber. This indirect determination was based on the presumed proportionality of average dampness to directly-measured capacitance or AC-conductivity. Proponents of this approach held that an accurate measurement exceeding a certain fixed threshold value would indicate a urine-soiled condition. They also held that such would be appropriate and sufficient to determine that a diaper needed changing. To be even partially correct, however, this assumption required that the portion of absorbent material actually measured be truly representative of the average dampness in the entire absorber volume. Also for meaningful measurements, that portion would have to be held in a constant shape and position, relative to the sensing means. Furthermore, selecting an appropriate fixed threshold value (that would remain valid with different sizes and applications of diapers) may not be possible. Thus, making sufficiently accurate and meaningful measurements (under all expected conditions) presented serious and unanswered practicality problems. These problems result from variations in measurable conductivity or capacitance due to many factors such as high humidity, perspiration, residual dampness from the washing of soiled skin, and the relative movement and random compression of the absorber as the wearer shifts position—all of which are likely to be experienced in the use environment.
In U.S. Pat. No. 5,469,145 (Johnson), the use of capacitive coupling of a sensing circuit (disposed on the outside of a diaper) to the material to be measured (inside the diaper) eliminated all direct connection between the monitoring device and the inside of a diaper. However, the described relatively high-impedance capacitor input to a monitor circuit would likely be particularly prone to external electrical noise and interference, as well as to significant capacitance variations due to unpredictable moisture distribution, the presence of other nearby conductive surfaces and physical movement—as the diaper wearer actively and continually shifts position. In short, all the previously described difficulties associated with other distributed dampness measurement approaches would tend to be worsened with the sensing elements moved farther away from the measurement volume. In addition, the use of continuous sinusoidal AC signals for sensing also typically entails greater energy consumption than does the use of DC conductivity methods. In prior systems this has required either the recharging or replacement of batteries, and thus complicated or precluded the use of a permanently sealed monitor unit.
Moreover, the prior systems were all ineffective for detecting the feces-soiling of diapers. Only a minuscule change in DC-conductivity or absorbent-bulk AC-conductivity (or capacitance) results from a small quantity of fecal matter on the surface of a diaper. This has rendered it typically undetectable by prior methods relative to much larger background changes produced by many of the above-described factors in the use environment. In general, the prior devices' collective inability to reliably detect feces stems from both the physical nature of the sensors and the electronic systems employed with them.
As described above, prior electronic systems have measured either DC or AC-conductivity or capacitance to detect urine. DC systems for accurately measuring liquid ionic conductivity typically require some “latching” means (such as circuits which detect an initial event and then remain “triggered”), because the applied electric field used for measurement causes dissociation of the very ions that enable electrical conduction, thus decreasing the measured conductivity over time. This effect poses only a minor problem when liquid urine directly bridges two closely spaced contacts, because the sudden initial increase in conductivity is substantial (due to the relatively high uric acid ionic concentration in urine) and this sudden increase can be easily differentiated from the baseline “dry diaper” condition. However, neither proportional bulk moisture content distributed in a diaper, nor the presence of feces, are suitable for direct DC-conductivity measurement. Particularly with feces, the ionic concentration is much lower than with direct liquid urine contact—and the water content, which allows the ions mobility, is often much lower in semi-solid waste. If a steady-state voltage is applied in an attempt to detect feces by inducing a DC current, the ionic dissociation effect results in rapid reduction in measured conductivity. With DC sensing of urine, a reference alarm threshold can be chosen such that the alarm condition will persist for a reasonable time—but probably not in all cases. This approach does not work at all with feces, however, because the initial conductivity is so low—and the decrease is so rapid—that after mere seconds, the conductivity falls below a practically measurable level. If a “latching” electronic detector is used to circumvent this problem—and is made sufficiently sensitive for detection of feces—this type of circuit may be easily triggered by momentary and insignificant conditions. Should this occur in actual use situations with a diaper monitoring system, caregiver intervention would likely be required to reset it. Because the true state of the diaper could not, in such cases, be reliably determined (without reverting to traditional diaper inspection), latching-type detectors are undesirable for use in elimination-absorber monitoring systems.
An additional problem is presented by the appropriate alarm criteria for feces-soiling. Since a diaper does not absorb feces and carry it away from direct contact with the skin (as it does with urine), and particularly given the irritation resultant from prolonged contact, feces must be detected virtually at the diaper surface—and a feces-soiled diaper needs to be changed as quickly as is practical. Obviously, for feces detection purposes, the various prior AC bulk-dampness type of sensors were not useful, as their sensing elements focused on a bulk volume of a diaper, not on its surface. On the other hand, a sensor structure involving exposed electrodes placed on the top surface of a diaper, while not only disconcerting to a caregiver, would prematurely respond to the presence of any urine. Such arrangement would also greatly increase the likelihood of false alarms resulting from bridging of the electrodes through either AC-coupling, or direct contact with skin, particularly if damp. As discussed above, feces are relatively very low in conductivity, and are thus difficult for such a system to reliably detect in the use environment. The overall elimination-absorber feces-detection problem is even more difficult, because a truly practical system must effectively combine the determination of both feces and urine-soiling of diapers. Clearly, no prior system has successfully done so.
The absence of any widely marketed consumer product for elimination-absorber monitoring further highlights the unsuitability of prior inventors' attempts. Today's parents and caregivers are still embarrassed by sniffing our kids and pulling their pants down in public to see whether they need to be changed. Thus, the desire remains for a truly effective, economic, safe, reliable, convenient, and energy efficient system for use with infants and other individuals dependent on a caregiver. These and other objectives, as will become apparent from the following specification and drawings, are satisfied by the present invention.